We hope to identify subpopulations of lymphocytes participating in various immunological reactions in order to gain an understanding of the physiology of the immune system. We will investigate the nature of hormonal influences on the immune system by identifying their sites of action. Work investigating the nature of cells which are able to stimulate in MLC is currently being extended to systems of restricted genetic differences. Such studies are intended to better define the nature of genetic and cell surface determinants relevant to cell interaction and recognition.